A level Statistics doubt??Post your doubts here!

[kevo123]

12/30+13/30....this is because the initial 12 females includes the females who watch kops are kids so they meet all the criterial and so the only other criteria to meet is the men who watch kops are kids which are 13..
(12/30)+(13/30)

Thanks!

 

[kevo123]

HARDEST QUESTION EVER!
http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_w12_qp_61.pdf
question 5ii)

 

[iFuz]

HARDEST QUESTION EVER!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_61.pdf
question 5ii)

2 boxes are chosen
so 6C2 to choose other two out of remaining
and 4! to get total arrangements.

6C2 x 4! = 360

 

[shafayat]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_63.pdf
Q6/c urgent help!

hey I am not really sure but !!
0.33x(.67)^7
bcuz the first youre choosing from all the three so 1/3 = 0.33 but the next ones cannot be the choosen one , they have to be from the other two so 2/3 = 0.67

 

[Kumkum]

Rutzaba
question 7ii
hope my handwriting is fine

 

[Ryan123]

HARDEST QUESTION EVER!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_61.pdf
question 5ii)

profits can be eitehr -(24*20) or (450*10-24*200
which are -480 or 4020
its -480 if more than 1 firework fails to work since they get no revenue and only have the cost. From the prev question you found out the prob for failure of more than 1 firework to be 0.264
its 4020 profit when less than 1 firework fails to work since they get the revenue..In this situation the prob is (1-.2640
y -480 4020
p .264 .736
do the E=(4020*.736)+(-480*.264)=2832

 

[Rutzaba]

View attachment 27242
Rutzaba
question 7ii
hope my handwriting is fine

thankyou soooooooooooooooooooooooooooooooooooooooooooooo much

 

[Kumkum]

thankyou soooooooooooooooooooooooooooooooooooooooooooooo much

not a problem
but I couldn't do the others sorry..

 

[kevo123]

profits can be eitehr -(24*20) or (450*10-24*200
which are -480 or 4020
its -480 if more than 1 firework fails to work since they get no revenue and only have the cost. From the prev question you found out the prob for failure of more than 1 firework to be 0.264
its 4020 profit when less than 1 firework fails to work since they get the revenue..In this situation the prob is (1-.2640
y -480 4020
p .264 .736
do the E=(4020*.736)+(-480*.264)=2832

ohhh, makes sense. Thanks!

 

[lisahamed]

i tried it that way, doesnt match, the examiners report says to use 0.97 as the probability :S

 

[shafayat]

as far as i know the first can be any colour so its prob is 1 and the one after that cant be the same colour so it will be 2/3 followed by 2/3 until the rest 7 slots are filled....as a result the ans is (2/3)^7

okei !! this seems more correct .. thanks for correcting me

 

[lisahamed]

within 12g means
20+12 and 20-12
so P( 8< 32 ) = 0.94
now standardize this and solve

within 12g means
20+12 and 20-12
so P( 8< 32 ) = 0.94
now standardize this and solve

i tried it that way, doesnt match, the examiners report says to use 0.97 as the probability :S

 

[aleezay]

" The masses of articles produced in a particular workshop are normally distributed with mean 51.3 g and standard deviation 20.5 g. Find the symmetrical limits, about the mean, within which 75% of the masses lie."

someone PLEASE explain!
[ans: a=27.7 , b=74.9]

I'm not sure if your problem has already been addressed, but your question is too interesting to resist So here goes..
Symmetrical limits means that both the values, let them be x and y are the same distance from the mean. That means x-mean and y-mean are the same but with opposite signs. like for 3 and 1c about 2.. 3-2=1 and 1-2=-1
So P(x< X < y) = .75
P[(x-51.3)/20.5< X < (y-51.3)/20.5] = .75
this brings us to
P(-a< Z <a) = .75
2*Fi(a)-1= .75
Fi(a) = .875
so a is approximately 1.152
(x-51.3)/20.5= 1.152 and x=74.9
(y-51.3)/20.5= -1.152 and y=27.7

 

[shafayat]

View attachment 27242
Rutzaba
question 7ii
hope my handwriting is fine

hey! Can you tell me y did u take Z as negative ? it could have been positive also ?

 

[lisahamed]

I'm not sure if your problem has already been addressed, but your question is too interesting to resist So here goes..
Symmetrical limits means that both the values, let them be x and y are the same distance from the mean. That means x-mean and y-mean are the same but with opposite signs. like for 3 and 1c about 2.. 3-2=1 and 1-2=-1
So P(x< X < y) = .75
P[(x-51.3)/20.5< X < (y-51.3)/20.5] = .75
this brings us to
P(-a< Z <a) = .75
2*Fi(a)-1= .75
Fi(a) = .875
so a is approximately 1.152
(x-51.3)/20.5= 1.152 and x=74.9
(y-51.3)/20.5= -1.152 and y=27.7

could u please help me out with this one? it seems kinda odd http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_w11_qp_61.pdf no.5 i
the examiners report says to use 0.97 as the probability... cant think of as to why :S would be very thankful!

 

[aleezay]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_62.pdf
Question 7)ii)
if somebody can please explain this to me please.

What exactly troubles you in this q? Its simple
P(X<0) giving you P(Z<(0-u)/2u)) i.e P=(Z<-0.5)
Now solve it like any other q

 

[aleezay]

could u please help me out with this one? it seems kinda odd http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_61.pdf no.5 i
the examiners report says to use 0.97 as the probability... cant think of as to why :S would be very thankful!

It IS .97.. but later on..
see the q starts the same way as your previous q. So I think you wont mind if I jump to
P(-a< Z < a) = .94
2*Fi(a) - 1= .94
Fi(a) = .97
I think its THIS .97 that they are referring to.. since taking .97 at the start does not lead to the right answer..

 

[Lujain M.]

It IS .97.. but later on..
see the q starts the same way as your previous q. So I think you wont mind if I jump to
P(-a< Z < a) = .94
2*Fi(a) - 1= .94
Fi(a) = .97
I think its THIS .97 that they are referring to.. since taking .97 at the start does not lead to the right answer..

I have the same doubt but i dont understand why do we have to do this step to get 0.97 ? Like what is clue for me to do this step?

 

[Champ101]

Hey guys good luck.for stats today..I hope we all can tackle it easily n get good marks...all the best

 

[shafayat]

I have the same doubt but i dont understand why do we have to do this step to get 0.97 ? Like what is clue for me to do this step?

There really isn't any clue ! Its just how u solve a question !
But to help yourself you can draw up a bell shaped curve
So u get something like
Phi(a)-phi(-a)
Which is
Phi(a)-(1-phi(a))
So expand brackets
2phi(a)-1=0.94
Now solve and find value of a